Fig. 3.

Stimulation of pharyngeal pumping by E. coli OP50. A. Representative example of simultaneous EPG recordings from seven N2 worms (numbered 1 to 7) in one chip; each trace from a different worm. Baseline activity recorded in M9 was followed by switching (vertical bar masks electrical artifact) to OP50 (O.D.₆₀₀ = 4) in M9; the switch marked the termination of a 2-h period of food deprivation. Pumping increased and occurred in irregular bouts. Worms 1 and 5 were head-first in worm traps while the others were tail-first. B. Time course of pumping stimulation by OP50. Perfusate switch occurred at the vertical dotted line, with the electrical artifact blanked. Lines show mean pump frequency in worms perfused with OP50 at O.D.₆₀₀ values between 0 (blank control) to 5 (n = 19–33 worms/group). Concentrations are denoted by color (see key). C. Concentration-response curves for rapid and sustained responses to OP50. Plots show mean pump frequency measured from t = 2–7 min (open circles and dashed line; rapid response) or t = 30–60 min (filled circles and solid line; sustained response) following the switch to OP50. The lowest OP50 concentration tested (O.D.₆₀₀ = 1) evoked nearly half-maximal pump frequencies, which implies that C_1/2 ≅ 1 mM for both rapid and sustained responses, but more data would be required to accurately constrain C_1/2 and the Hill coefficient. The smooth curves in Fig. 3C, which are best fits to the Hill equation calculated assuming a Hill coefficient = 5, show saturating values of 3.37 Hz and 2.55 Hz for rapid and sustained responses, respectively. D. Effect of OP50 on pump frequency and amplitude. Data from worms perfused with OP50 between O.D.₆₀₀ = 2–5 were combined and plotted as mean pump frequency (solid line) and peak-to-peak amplitude (dashed line; n = 90 worms). Switch to OP50 occurred at the vertical dotted line, with the electrical artifact blanked. E. IPI probability density histogram for worms perfused with OP50 between O.D.₆₀₀ = 2–5, from t = 30–60 min (n = 90 worms). The mode of the distribution is marked (arrow; 205 ms, or 4.89 Hz). Plots in panels B-E are from the same groups of worms. Some error bars are smaller than the symbols. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)